The horizontal continuous casting process has provided substantial benefits in the metal fabricating arts and is particularly appreciated for its ability to produce extended length constant cross-section castings or billets which would be generally impractical if attempted using other more conventional casting systems. While the structures of horizontal continuous casting systems vary substantially, generally all include a large capacity insulated reservoir for molten metal referred to as a tundish. The most common tundish fabrication includes an interior lining of refractory material chosen for its extreme resistance to the high temperatures associated with metal casting. The tundish is further provided with an outlet orifice near the lower portion of the tundish and provision is made to couple a casting mold and communication with the tundish such that molten metal may be transferred from the tundish interior to the mold. Mold structures vary somewhat but generally all comprise elongated metal structures defining a central passage therethrough and are usually formed of a metal such as copper having a high heat transfer characteristic. The center mold passage is surrounded by a water cooled jacket which in turn is coupled to a supply of cooling water having sufficient flow to carry the heat from the mold passage during the casting process. The molten metal is introduced into the cooled mold and is solidified or frozen therein to form the casting. In most instances, a dummy or starter bar is inserted into the mold passage and coupled to a casting puller arrangement to initiate the casting process. As the process begins, the starter bar is withdrawn from the mold through the mold passage and the metal within the tundish is permitted to flow into the mold passage. Within the mold passage, the casting forms in a welded attachment to the starter bar. The casting pullers thereafter extract the casting formed within the mold in accordance with a predetermined motion profile in which the casting emerges from the mold and is continuously formed or cast as metal within the tundish flows into the casting mold to replace the withdrawn casting.
In most horizontal continuous casting systems, the motion profile used by the puller systems to extract the casting forming within the mold is a series of forward or outward motions interleaved with brief and relatively small reverse motion steps. The latter are generally provided to assure proper formation of the continuous casting. In many horizontal continuous casting systems, a slide gate is interposed between the tundish outlet and the casting mold to provide a shut-off valve mechanism. The most common slide gate includes a pair of ceramic plate members which may be interchanged. One ceramic plate defines an aperture therethrough while the other is completely closed defining no aperture. Closure of the slide gate is provided by inserting the plate having no aperture while opening of the slide gate is provided by inserting the plate having an aperture therein.
Ideally, it would be desirable to operate a horizontal continuous casting system in a virtually endless extended operation in which equilibrium is reached and casting takes place continuously and in which the supply of molten metal within the tundish is periodically replaced. Unfortunately, several factors limit the extent to which a horizontal continuous casting system may be operated in an uninterrupted manner. One of the most significant limitations upon the duration of horizontal continuous casting operation is the substantial wear imposed upon the continuous casting mold. Within the mold, a ceramic ring generally known as a break ring is used to interface the slide gate to the mold and is subject to substantial wear during the normal casting process. In addition, the mold itself is usually formed of a copper metal or the like which has a significant tendency to wear as the forming casting is drawn through the mold passage. Other factors such as breakdown or failure of the mold which compromise its integrity or safety also frequently force shutdown of continuous casting operations. In addition to mold problems, however, other factors within the horizontal continuous casting systems of the type to which all mechanical and electromechanical systems are subject, contribute to periodic shutdown of the casting operation.
A substantial number of problems arise when a horizontal continuous casting system is prematurely shutdown which have severe impact upon the economics of casting operation. Shutdown itself is accomplished relatively simply in systems having slide gate apparatus by the insertion of the apertureless ceramic plate which terminates the flow of molten metal into the mold. The problems associated with such shutdowns, however, are substantial. Almost immediately upon the termination of the casting process, the molten metal within the tundish begins to cool and approach its freezing temperature. This freezing problem is particularly critical in the tundish region near the slide gate itself. While practitioners may delay this freezing process somewhat through the use of high energy plasma torches or induction coils, the metal freezing within the slide gate area is virtually impossible to prevent and, in any extended shutdown, renders restarting of the casting operation impossible.
Thus, while horizontal continuous casting operations may survive brief interruptions of the casting process, any extended duration shutdown forces a complete termination of the casting operation. Thus, once the operator has determined that the interruption of casting operation will force a complete shutdown, the tundish must be completely emptied to prevent the slide gate area from freezing off and exacerbate the problems of restarting. In addition, the refractory lining of the tundish must be inspected and repaired in preparation for the next casting operation. The refractory lining within the tundish tend to form small cracks due to its ceramic character during the casting process. These cracks, in turn, become filled with molten metal as the tundish supply of molten metal is maintained. Upon shutdown and cooling, the molten metal within these cracks freezes to form metal "fins" extending into the refractory lining. These metal fins must be extracted from the refractory lining and the lining cracks patched using a repair material before the tundish is again used in the continuous operation. In addition, the ceramic material of the slide gate mechanism is subject to fatigue and cracking and thus must often be replenished and replaced before casting may be resumed.
The recognition by practitioners of the art of the severe economic impact of premature or undesired shutdown of casting operations has prompted practitioners to attempt the development of systems which maintain the molten metal within the tundish and which accomplish the restoration of the casting process with sufficient speed to avoid the freezing of molten metal within the tundish slide gate area and permit the restarting of the casting operation. Such systems have included providing heated tundishes and heated slide gate arrangements as well as systems intended to speed up the removal and replacement of a worn or failed casting mold. Unfortunately, however, most systems devised have been relatively ineffective and unsuccessful.
There remains, therefore, a need in the art for an improved horizontal continuous casting system which facilitates the rapid change-over of horizontal continuous casting molds and which avoids the complete termination of casting operations by permitting the casting operation to be restarted.